THE MAKING OF CHESHIRE (_cont._). II
THE OLDER ROCKS
Let us now visit some quarries in East Cheshire. We shall find
considerable difficulty in reaching some of them. It will be necessary
to get permission from the owners of the quarries, put on a special suit
of clothes, enter an iron cage, and descend many hundred feet perhaps
into the depths of the earth's surface until we find ourselves--in a
coal-mine!
[Illustration: SECTION OF ROCKS FROM KNUTSFORD TO BUXTON]
Unlike the New Red Sandstones, which are found for the most part in flat
horizontal beds, the coal beds slope downwards from east to west. This
is due to the uplifting of the East Cheshire hills, which we shall
presently explain. When this uplift took place, the coal beds, which
were originally flat, became raised in the east and equally lowered in
the west. When the sea flowed over them they became covered by sandy
deposits of such a thickness that in the greater part of Cheshire the
coal cannot be reached. The earliest sands laid down formed what are
called the Permian rocks, and the later layers the New Red Sandstone
series mentioned in the last chapter. The Permian rocks may be well seen
at Stockport, in the river beds of the Tame and the Goyt which have cut
their way through them. In the strip of country between Stockport and
Macclesfield, and again on the south-eastern borders of Cheshire, the
upturned edges of the coal beds have been left exposed so that the coal
is near the surface and can be easily extracted.
Coal consists of the vegetable remains of forest trees and their
undergrowth. If you look at a lump of coal you will see that it has been
pressed down into thin layers like the leaves of a book. When these
layers are split apart there are often found the fossil remains of
leaves and roots of trees, fronds of ferns, seed-cones and stems of
plants which grew in the forests. Some of these, particularly the ferns,
are often of great beauty. You may see a number of these 'coal pictures'
in the Vernon Park Museum at Stockport. Here too you will find portions
of the actual trunks of trees that have been dug up just where they
stood when the seas flowed over them.
You may learn even to distinguish different varieties of these forest
trees, just as you are able to distinguish the oak and the beech and the
elm of to-day. Latin names such as Sigillaria, Lepidodendron, and
Salisburia have been given to them. The most beautiful of all is a
Maidenhair Tree-fern. The Calamites was a huge 'Horse-tail' plant of
which you may find small varieties to-day on banks and in hedgerows.
On the coast of Wirral, between Meols and New Brighton, are the remains
of a forest which has only in very recent years been covered by the sea.
Boys who live in this neighbourhood may have heard their parents tell of
the stumps of tree-trunks sticking out through the sands when the tide
was low. This shows that the land is continually undergoing changes, at
one time being raised above the seas, at another time sinking beneath
the waves.
The beds or 'seams' of coal vary in thickness from a thin film to
several yards, and are separated from one another by layers of hard
clays and flagstones. From the flagstone beds are obtained the square
slabs with which the pavements of our towns and cities are laid. In many
of the quarries near the Cheshire coal-field you may watch the workmen
cutting and shaping these stones.
The beds of clays and seams of coal make up what are called the 'Coal
Measures'. These in their turn rest upon a foundation of hard rock,
harder than any we have yet examined, called Millstone Grit or
Gritstone. Boys who live in the hilly parts of East Cheshire are very
familiar with it, for very probably the houses in which they live and
the churches and chapels where they worship have been built of this
stone. It is composed of coarse sand and grit, and, like the red
sandstone, is a waterlaid deposit several thousand feet in thickness.
The Pennine Hills, on the borderland of Cheshire and Derbyshire, are
covered with Millstone Grit, which has been thrust upwards by the
crumpling and arching of the rocks beneath it.
Below the Gritstone are still older rocks of a different character
called the Limestone series. The uppermost beds contain layers of a
sandy substance called Yoredale sandstones. Mixed with them are layers
of shale, a dark bluish grey clay that crumbles into thin fragments when
crushed with the hand, and thin seams of limestone and, occasionally, of
coal. These are the oldest rocks that are found anywhere in Cheshire.
You may see them in the hills east of Macclesfield and Congleton and the
higher parts of Longdendale. Below these beds is a mass of Mountain
Limestone which has been forced upwards into an arch by tremendous
pressure of rocks from either side, and has lifted up the Gritstone
above to a height of nearly two thousand feet. In this way the
highlands of East Cheshire, and indeed the whole of the Pennine Chain,
have been formed. The Mountain Limestone, which consists almost entirely
of animal remains, especially shells and corals, extends right under the
highest hills of Cheshire, and comes to light in the cliffs of the
beautiful dales of Derbyshire. Only at one spot, a quarry near Astbury,
does it appear at the surface in Cheshire.
The Coal Measures, Millstone Grit, Yoredale sandstones, and Mountain
Limestone make up what geologists call the Carboniferous or Coal-bearing
series, so called because in England our chief supplies of coal are
obtained from this group of rocks.
But we should have to dig deeper even than the Mountain Limestone before
we could reach the original surface of the earth in Cheshire. Long ages
ago, ages so distant that not even the most learned men of science can
reckon them, our earth was a globe of fiery molten rock. As the surface
gradually cooled it became wrinkled, as a baked apple will when taken
from an oven. Water collected in the hollows into which fragments of
rock were washed down from the ridges, and thus the waters were raised
and formed into seas and lakes. But we shall not find any of these rocks
in Cheshire, though you may see them in great masses in the mountains of
Cumberland and Wales, where they have been forced upwards by the violent
movements always at work in the interior of the earth. It is of these
molten rocks that the mass of stone which was brought by the ice from
Cumberland and left on Eddisbury Hill is composed.